The presence of dopants within an insulating or semiconducting matrix can dramatically increase the electrical conductivity of the matrix. In some devices, these dopants move within the matrix in response to a programming electrical field. This dopant motion can dynamically alter electrical resistance of the matrix and influence the electrical operation of an associated electrical device. After removal of the programming electrical field, the location and characteristics of the dopants remain stable until the application of another programming electrical field. The dopants can be used as a “memory” of past electrical fields which were applied to the matrix.
Electrical devices that exhibit this “memory” of past electrical conditions through dopant based changes in electrical resistance have been called “memristors” or “memristive devices.” Memristive behavior is most strongly evident in nanometer scale devices and could potentially be used for high density data storage, circuit calibration, or to model biological processes such as nerve synapses. To more closely approximate complex interactions, it can be desirable for memristive devices to have multiple state variables which are at least partially decoupled.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.